// -*- C++ -*-
/*
 * SPDX-FileCopyrightText: Copyright (c) 2022 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
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 * NVIDIA SOFTWARE LICENSE
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 * 15. ENTIRE AGREEMENT. This license is the final, complete and exclusive agreement between the parties relating to the subject matter of this license and supersedes all prior or contemporaneous understandings and agreements relating to this subject matter, whether oral or written. If any court of competent jurisdiction determines that any provision of this license is illegal, invalid or unenforceable, the remaining provisions will remain in full force and effect. This license may only be modified in a writing signed by an authorized representative of each party.
 *
 * (v. August 20, 2021)
 */

#ifndef _CUDA_FUNCTIONAL_
#define _CUDA_FUNCTIONAL_

#include <cuda/std/type_traits>
#include <cuda/std/functional>
#include <cuda/std/utility>

_LIBCUDACXX_BEGIN_NAMESPACE_CUDA
namespace __detail
{

template <class _Ret, class _DecayFn>
class __return_type_wrapper {
 private:
  _DecayFn __fn_;

 public:
  __return_type_wrapper() = delete;

  template <class _Fn,
            class = _CUDA_VSTD::__enable_if_t<_CUDA_VSTD::is_same<_CUDA_VSTD::__decay_t<_Fn>, _DecayFn>::value>>
  _LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX11
  explicit __return_type_wrapper(_Fn &&__fn) noexcept
    : __fn_(_CUDA_VSTD::forward<_Fn>(__fn)) {}

  template <class... _As>
  _LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX11
  _Ret operator()(_As&&... __as) & noexcept {
#if !defined(__NVCC__) || defined(__CUDA_ARCH__)
    static_assert(
        _CUDA_VSTD::is_same<
            _Ret,
            typename _CUDA_VSTD::__invoke_of<_DecayFn&, _As...>::type
          >::value,
        "Return type shall match the proclaimed one exactly");
#endif

    return _CUDA_VSTD::__invoke(__fn_, _CUDA_VSTD::forward<_As>(__as)...);
  }

  template <class... _As>
  _LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX11
  _Ret operator()(_As&&... __as) && noexcept {
#if !defined(__NVCC__) || defined(__CUDA_ARCH__)
    static_assert(
        _CUDA_VSTD::is_same<
            _Ret,
            typename _CUDA_VSTD::__invoke_of<_DecayFn, _As...>::type
          >::value,
        "Return type shall match the proclaimed one exactly");
#endif

    return _CUDA_VSTD::__invoke(_CUDA_VSTD::move(__fn_),
                                _CUDA_VSTD::forward<_As>(__as)...);
  }

  template <class... _As>
  _LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX11
  _Ret operator()(_As&&... __as) const& noexcept {
#if !defined(__NVCC__) || defined(__CUDA_ARCH__)
    static_assert(
        _CUDA_VSTD::is_same<
            _Ret,
            typename _CUDA_VSTD::__invoke_of<const _DecayFn&, _As...>::type
          >::value,
        "Return type shall match the proclaimed one exactly");
#endif

    return _CUDA_VSTD::__invoke(__fn_, _CUDA_VSTD::forward<_As>(__as)...);
  }

  template <class... _As>
  _LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR_AFTER_CXX11
  _Ret operator()(_As&&... __as) const&& noexcept {
#if !defined(__NVCC__) || defined(__CUDA_ARCH__)
    static_assert(
        _CUDA_VSTD::is_same<
            _Ret,
            typename _CUDA_VSTD::__invoke_of<const _DecayFn, _As...>::type
          >::value,
        "Return type shall match the proclaimed one exactly");
#endif

    return _CUDA_VSTD::__invoke(_CUDA_VSTD::move(__fn_),
                                _CUDA_VSTD::forward<_As>(__as)...);
  }
};

}  // __detail

template <class _Ret, class _Fn>
inline _LIBCUDACXX_INLINE_VISIBILITY
__detail::__return_type_wrapper<_Ret, _CUDA_VSTD::__decay_t<_Fn>>
proclaim_return_type(_Fn&& __fn) noexcept {
  return __detail::__return_type_wrapper<_Ret, _CUDA_VSTD::__decay_t<_Fn>>(
      _CUDA_VSTD::forward<_Fn>(__fn));
}
_LIBCUDACXX_END_NAMESPACE_CUDA

#endif // _CUDA_FUNCTIONAL_

